The most important objective in this research is to study the metabolism of NG-monomethyl-L-arginine, an endogenously synthesized compound, and to identify one of the metabolites as N-methylurea, a compound which can be nitrosated to give rise to 1-N-methyl,1-N-nitrosourea, one of the most potent carcinogens known. This will be pursued with the following aims: (1)\to study the metabolic pathways of NG-monomethyl-L-arginine which involve hydrolytic cleavage, oxidative demethylation, and decarboxylation; (2)\to investigate the possible formation of N-methylurea from NG-monomethyl-L-arginine; (3)\to further purify protein methylase I which methylates the guanadine group of protein-bound arginine residues; and (4)\to investigate the possible antitumor effects of NG-monomethyl-L-arginine on tumor cells in tissue or cell culture. (K)